Patent GB-742593-A (GB)
Title: Improvements in or relating to electronic apparatus for use in electric pulse code modulation signalling systems
IPC: H03M1/00
Filed: 1953-01-20
Abstract: 742,593. Electric selective signalling. GENERAL ELECTRIC CO., Ltd., BAYLISS, A. J., and PEDDLE, E. A. R. Jan. 12. 1954 [Jan. 20, 1953], No. 1656/53. Class 40(1) Electronic apparatus for encoding or decoding in a pulse-code-modulation-signalling system, comprises a set of like cold cathode discharge tubes the main discharge paths of which are connected in parallel between one pole of a stabilized H.T. source and a utilization device, the other side of which is connected to the other pole of the H.T. source. The tubes are controlled independently, and when conducting cause a current of predetermined value to flow in the utilization device, the predetermined current values associated with the respective tubes depending on the quantized value associated with a corresponding one of the time positions in a pulse code group of the system. As shown in Fig. 1, highly stable cold cathode triodes 1a, 1b, 1c,... &c. are connected in series with the utilization device 15 across a stabilized H.T. source applied between terminal 3 and ground, the tubes being' fired independently when positive pulses are applied to the respective trigger grids over terminals 7a, 7b, 7c.... &c. The resistors 9-10, 11-12, 13-14, &c. are so di-. mensioned that when the tubes conduct, they pass substantially equal currents, but the currents flowing through the associated resistors 10, 12, 14... &c. and summed in the utilization device bear a predetermined ratio, e.g. 1: ¢: “; ... &c., when the binary system is used. When used as a decoder, the respecitive terminals 7a, 7b,... &c. would be pulsed dependent on whether or not a pulse occurred in the first, second... &c: positions of a received pulse code group, so that the current flowing in the utilization device would, at the end of a signal, give the analogue value of the binary number received. Zeroizing is effected by opening a contact 2 to deenergize the conducting tubes. The device would be used for encoding, as described in Specification 713,476. To ensure a constant current load on the stabilized H.T. source, each tube 1a, 1b, 1c,... &c is associated with a cold cathode discharge tube 16a, 16b, 16c... &c., Fig. 2, to form a bistable trigger circuit. In the datum (or zero) position the tubes 16a. 16b ... &c. conduct. these tubes being blocked as the associated tubes 1a, 1b, 1c, ... &c. are fired by pulses on the respective stage input terminals 7a, 7b....&c. Zeroizing is effected in this case by applying a positive pulse over terminal 23 to fire all the " zero " tubes 16a, 16b.... &c. This arrangement may be modified, Fig. 3, by supplying the anodes of both tubes in each stage over a resistor 24a, 24b, 24c... &c. in the event that the stabilized supply voltage is greater than the anode-cathode breakdown voltage of the tubes. In a further modification Fig. 4, (not shown), each stage consists of a high stability cold cathode diode and a pair of cold cathode triodes forming a trigger circuit, the latter being switched from its zero condition to the other. by the stage input pulse applied to one trigger grid and zeroized by a pulse applied to the other trigger grid. The diode fires as the trigger circuit goes to its " one " position and controls the current flow to the utilization device. The manner in which the arrangement of Fig. 3 could be used in the telemetering system described in Specification 713.476 as a coder and as a decoder is described with reference to Figs. 6. 5 (not shown). Specifications 703.578 and 718,058, [Group XL(c)], also are referred to.